AbstractThe relationship of age and a life style of physical activity with isometric knee extension strength and a simple and choice resisted response time was examined in 60 male subjects divided into four equal groups: Old Active, Old Inactive, Young Active, Young Inactive. Each response measure consisted of a visual reaction time followed by a movement to a target. Reaction time was further fractionated into premotor and motor time components. Resistance was applied in reaction time trials via an electromagnet placed below the subject's heel. Although knee extension strength was lower in old groups, the Old Actives were 7.7 kg stronger than Old Inactives. Simple and choice total reaction time for all groups lengthened in the resisted condition due to an increased motor time component. Even though the resistance applied was a fixed 10% of maximum strength the increase in resisted motor time was greatest for the young groups and unrelated to physical activity level.